Electrosurgical generator

ABSTRACT

An electrosurgical system for performing an electrosurgical procedure is provided and includes an electrosurgical generator and a calibration computer system. The electrosurgical generator includes one or more processors and a measurement module including one or more log amps that are in operative communication with the processor. The calibration computer system configured to couple to a measurement device and is configured to measure parameters of an output signal generated by the electrosurgical generator. The calibration computer system is configured to compile the measured parameters into one or more data look-up tables and couple to the electrosurgical generator for transferring the data look-up table(s) to memory of the electrosurgical generator. The microprocessor is configured to receive an output from the log amp(s) and access the data look-up table(s) from memory to execute one or more control algorithms for controlling an output of the electrosurgical generator.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrosurgical generator. Moreparticularly, the present disclosure relates to electrosurgicalgenerators having a gain calibrated RF logarithmic amplifier sensor.

2. Description of Related Art

RF generators configured for use with electrosurgical instruments areknown in the art. In certain instances, one or more logarithmicamplifier, sometimes referred to as “log amps,” may be incorporated intothe circuitry of the RF generators to compress a large dynamic inputrange to a more manageable output for a digital signal processor of theRF generator. For example, a typical log amp can have an input rangethat varies by 10,000 times, e.g., from about 100 μV to about 1V.Conversely, a log amp output, typically, varies by 3 times, e.g., fromabout 1V to about 3V. To accomplish these log amp input and outputratios, log amps typically have a very high gain bandwidth, which isfairly constant. Due to internal construction of the log amps, however,the log amps have non-linear gain dependency at their inputs, which, inturn, results in decreased accuracy of log amp sensors associated withthe log amps.

SUMMARY

In view of the foregoing, there exists a need for RF generators havingone or more gain calibrated log amp sensors configured to compensate forgain variance at the input of the log amp.

Aspects of the present disclosure are described in detail with referenceto the drawing wherein like reference numerals identify similar oridentical elements. As used herein, the term “distal” refers to theportion that is being described which is further from a user, while theterm “proximal” refers to the portion that is being described which iscloser to a user.

An aspect of the present disclosure provides an electrosurgical systemfor performing an electrosurgical procedure. The electrosurgical systemincluding an electrosurgical generator that includes at least oneprocessor and a measurement module including at least one log amp inoperative communication with the processor. A calibration computersystem is configured to couple to a measurement device and is configuredto measure parameters of an output signal generated by theelectrosurgical generator. The calibration computer system is configuredto compile the measured parameters into at least one data look-up table,and couple to the electrosurgical generator for transferring the atleast one data look-up table to memory of the electrosurgical generator.The microprocessor is configured to receive an output from the at leastone log amp and access the at least one data look-up table from memoryto execute at least one control algorithm for controlling an output ofthe electrosurgical generator.

The at least one log amp may be configured to receive an output from asensor that is configured to sense an output of the electrosurgicalgenerator.

The measurement device may be a device that measures RMS current. Inthis instance, the measurement device may include a current toroid thatis configured to measure an output current of the electrosurgicaldevice.

The output from the at least one log amp may be a voltage output.

The parameters contained in the data look-up table may include gain ofthe at least one log amp, output voltage of the at least one log amp,input voltage of the at least one log amp, output current of theelectrosurgical generator and output voltage of the electrosurgicalgenerator.

The at least one control algorithm may be configured to calculate aslope and gain of the log amp. The slope and gain of the log amp may becalculated through a dynamic operating range of the log amp. The log ampmay be configured to allow a user to vary a slope thereof to obtain anoptimum slope through the dynamic operating range.

The control algorithm may utilize a piece-wise linear fit of the gainrelative to the measured output of the log amp to correct gainvariations of the log amp. Moreover, the control algorithm may utilizean averaging technique of the gain relative to the measured output ofthe log amp to correct gain variations of the log amp. Further, thecontrol algorithm may utilize a polynomial curve fitting technique ofthe gain relative to the measured output of the voltage log amp tocorrect the variations in gain.

The measurement module may include a voltage and current sensor that areconfigured to measure respective voltage and current on a patient sideof an output transformer of the measurement module. The voltage andcurrent sensors may be isolated from a patient and referenced to groundof the electrosurgical generator by isolating and/or reducing a voltagesense line with the use of one or more capacitors.

An aspect of the instant disclosure provides a computer calibrationsystem for calibrating measurement circuitry of an electrosurgicaldevice. The computer calibration system includes a measurement devicethat is configured to measure an output of the electrosurgical device. Amemory that stores measurement data includes a plurality of current andvoltage values of at least one log amp of the measurement circuitry, aplurality of gain values of the log amp, a plurality of current andvoltage values of the electrosurgical device and a plurality ofimpedance values of a load coupled to the electrosurgical device. Aprocessor may be configured to execute one or more control algorithms tocompile the measurement data into at least one data look-up table. Acommunication interface may be configured for transferring the at leastone data look-up table to memory of the electrosurgical device when thecomputer calibration system is coupled to the electrosurgical generator.

The at least one log amp may be configured to receive an output from asensor that is configured to sense an output of the electrosurgicaldevice.

The measurement device may be configured to measure RMS current. In thisinstance, the measurement device may include a current toroid that isconfigured to measure an output current of the electrosurgical device.

An aspect of the instant disclosure provides a method for calibratingmeasurement circuitry of an electrosurgical device. An output of theelectrosurgical device is measured. An output of at least one log amp ofthe measurement circuitry of the electrosurgical device is measured. Adata look-up table including measurement data obtained from themeasuring steps is compiled. A slope and gain of the at least one logamp is calculated based on the measurement data obtained from themeasuring step. At least one control algorithm utilizing the calculatedslope and gain is executed. A gain of the log amp based on an output ofthe log amp to calibrate the measurement circuitry is recalculated.

The at least one control algorithm may utilize a piece-wise linear fitof the gain relative to the measured output of the log amp to correctgain variations of the log amp. Moreover, the at least one controlalgorithm may utilize either an averaging technique or a polynomialcurve fitting technique of the log amp gain relative to the measuredoutput of the voltage log amp to correct the variations in gain.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described hereinbelowwith references to the drawings, wherein:

FIG. 1 is a perspective view of an electrosurgical system including agenerator, calibration computer system, and electrosurgicalinstrument(s) according to an embodiment of the present disclosure;

FIG. 2 is a block diagram of the electrosurgical system depicted in FIG.1;

FIG. 3 is a schematic diagram of an RF output stage of the generatordepicted in FIGS. 1 and 2;

FIG. 4 is graphical illustration of an output voltage of a log ampplotted against an input voltage of the log amp across the dynamic rangeof the log amp;

FIG. 5 is a block diagram of the electrosurgical system depicted in FIG.1 coupled to a measuring device and a test load; and

FIG. 6 is a table illustrating tabulated measured and calculated datataken across a dynamic range of a log amp depicted in FIG. 2.

DETAILED DESCRIPTION

Detailed embodiments of the present disclosure are disclosed herein;however, the disclosed embodiments are merely examples of thedisclosure, which may be embodied in various forms. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a basis for the claims and as arepresentative basis for teaching one skilled in the art to variouslyemploy the present disclosure in virtually any appropriately detailedstructure.

FIG. 1 is a perspective view of an electrosurgical system 2 thatincludes a calibration system 16 according to embodiments of the presentdisclosure. System 2 includes an electrosurgical generator 8 includingelectronic circuitry that generates radio frequency power for variouselectrosurgical procedures (e.g., sealing, cutting, coagulating, orablating). The electrosurgical generator 8 may include a plurality ofconnectors to accommodate various types of electrosurgical instruments,e.g., a forceps 4, pencil 5, etc., that are configured to deliver theelectrosurgical energy to tissue during a surgical procedure. In theillustrated embodiment, each of the forceps 4 and pencil 5 includes oneor more electrodes that are configured to provide electrosurgical energyto treat tissue. For example, forceps 4 may be configured as a bipolarelectrosurgical forceps including jaw members 10 and 12 (FIG. 1) havinga respective electrode 24, 26 (FIGS. 1 and 2) that are each connectableto the electrosurgical generator 8 via a cable 14 (FIG. 1). Alternately,the forceps 4 may be a monopolar electrosurgical forceps, in which caseone of the jaw members 10 and 12 includes an active electrode, and areturn electrode is operably supported on a return pad (not shown) thatis configured to contact a patient. In the illustrated embodiment,pencil 5 includes an active electrode 13, and a return electrode isoperably supported on a return pad (not shown) that is configured tocontact a patient. For the remainder of the discussion, electrosurgicalsystem 2 and calibration system 16 are described in terms of use with abipolar electrosurgical forceps 4.

FIG. 2 is a block diagram of an electrosurgical system 2, which includesthe generator 8, forceps 4 and calibration computer system 16 of FIG. 1.Briefly, generator 8 includes a controller 18, a high voltage powersupply 20, and a radio frequency output stage 22, which operate togetherto generate an electrosurgical signal to be applied to tissue throughelectrodes 24, 26 of forceps 4. Controller 18 includes a digital signalprocessor (DSP) 28, a main processor 30, and a memory 32. The controller18 may be any suitable microcontroller, microprocessor, PLD, PLA, orother digital logic device. Memory 32 may be volatile, non-volatile,solid state, magnetic, or other suitable storage memory.

The controller 18 may also include various circuitry that serves as aninterface between the main processor 30 and other circuitry within theelectrosurgical generator 8 (e.g., amplifiers and buffers). Thecontroller 18 receives various feedback signals that are used by themain processor 30 and/or the DSP 28 to generate control signals tocontrol various subsystems of the generator 8, including the HVPS 20 andthe RF output stage 22. These subsystems are controlled to generateelectrosurgical energy having desired characteristics for performingsurgical procedures on tissue, which is represented in FIG. 2 by a testload “L.”

The generator 8 includes an AC/DC power supply 34 that receives powerfrom an alternating current (AC) line source (not explicitly shown) andconverts the AC line power into direct current (DC), and, in turn,provides the DC power to an energy conversion circuit 36. The energyconversion circuit 36 then converts the DC power at a first energy levelinto DC power at a second, different energy level based upon controlsignals received from the controller 18. The energy conversion circuit36 supplies the DC power at the second, different energy level to the RFoutput stage 22. The RF output stage 22 converts the DC power into ahigh-frequency alternating current (e.g., RF), which may then be appliedto tissue.

In accordance with the instant disclosure, the electrosurgical generator8 includes a measurement module 21 (FIGS. 2 and 3) that is configured todetermine voltage, current, impedance, and power at a tissue site sothat the controller 18 can use these measurements to control thecharacteristics of the electrosurgical output. The measurement module 21includes a voltage sensor 38 and a current sensor 40 coupled to theoutput of the RF output stage 22 (FIG. 2). The voltage sensor 38 sensesthe voltage across the output of the RF output stage 22 and provides,via a log amp 46, an analog signal representing the sensed voltage to ananalog-to-digital converter (ADC) 42, which converts the analog signalrepresenting voltage into digital form (FIGS. 2 and 3). Similarly, thecurrent sensor 40 senses the current at the output of the RF outputstage 22 and provides, via a log amp 48, an analog signal representingthe sensed current to another ADC 44, which converts the analog signalrepresenting current into digital form (FIGS. 2 and 3).

The DSP 28 receives the sensed voltage and sensed current data from therespective log amps 46 and 48 and uses it to calculate the impedanceand/or the power at the tissue site. The main processor 30 of thecontroller 18 executes algorithms that use the sensed voltage, thesensed current, the impedance, and/or the power to control the HVPS 20and/or the RF Output Stage 22. For example, the main processor 30 mayexecute a PID control algorithm based upon the calculated power and adesired power level, which may be selected by a user, to determine theamount of electrical current that should be supplied by the RF outputstage 22 to achieve and maintain the desired power level at the tissuesite. As discussed in greater detail below, the DSP 28 utilizes one ormore control algorithms to calibrate the received sensed voltage andcurrent data to obtain a more accurate representation of the RMS voltage(Vrms) that is transmitted to the forceps 4.

FIG. 3 illustrates a block diagram of internal components of themeasurement module 21 including the voltage and current sensors 38 and40 connected to the RF output stage 22. Voltage and current sensors 38and 40 are measured on the patient side of an output transformer “T.” Inthe illustrated embodiment, both the voltage and current sensors 38 and40 are duplicated for redundant sensing (only one of each is shown). Thesensors 38, 40 are isolated from the patient and are referenced toground “G” of the generator 8 (FIG. 3). With respect to the voltage,this is accomplished by isolating and reducing a voltage sense line withthe use of a pair of capacitors C1 and C2 (FIG. 3). For the current, acenter tap transformer configuration is utilized including a pair ofblocking capacitors “BC” between the ground “G” of the generator 8 andtransformer “T”. The blocking capacitors “BC” are used as a currentsensing element instead of a traditional lossy element such as, forexample, a resistor. The isolation and signal reduction for the currentsense line is maintained using a pair of capacitors C3 and C4 (FIG. 3).The capacitors C1-C4 may be any suitable type of capacitors includingwithout limitations polyphenylene sulphide (PPS) film capacitors,ceramic chip capacitors NPO (COG) and the like. In accordance with theinstant disclosure, capacitors C1-C4 are ceramic chip capacitors NPO(COG) and are chosen for their voltage and thermal stability. Theaforementioned capacitor configuration facilitates maintaining aconsistent overall gain of the measurement module 21 and, in particularlog amps 46 and 48.

Log amps 46 and 48 may be any suitable type of log amp. A suitable logamp may be an AD8310 manufactured by Analog Devices (FIG. 3). Thisparticular log amp was chosen because of its low current draw (e.g.,approximately 8 mA), small footprint (e.g., approximately 4×5 mm), asuitable differential AC input that ranges from about −91 dBV to about 9dBV, a suitable DC level output that ranges from about 0.4V to about2.6V, and a large dynamic range that ranges from about −91 dB to about 4dB. The AD8310 log amp utilizes minimal external components as comparedto other log amps that are sometimes utilized in conventionalgenerators. Other suitable log amps that may be utilized in accordancewith the present disclosure include: AD8307, AD8318, AD8317, ADL5513,AD8363 (RMS) all manufactured by Analog Devices, HMC612LP manufacturedby Hittite, LTC5507 manufactured by Linear Technology, and TL441manufactured by Texas Instruments.

FIG. 4 shows a typical performance characteristic of an output of thelog amp 46. In accordance with the instant disclosure, a slope is usedto derive a linear slope equation in the form of y=mx+b, where m is theslope of the output of the log amp 46 and b is the intercept of the logamp 46 at a 0 dBV input. The X axis shows the input in dBV and the Yaxis shows the corresponding output of the log amp 46. Log amp 46includes a slope input (not explicitly shown) that gives the flexibilityto increase the slope of the thereof. In accordance with the instantdisclosure, to balance between input versus output range, the slope wasincreased to 40 mV/dB; this was done by adding a 23.2 KΩ resistorbetween two or more pins of the log amp 46. With the increased slope of40 mv/dB the output of the log amp 46 is 1.2V and an intercept point ofthe log amp 46 is 2.95 at the 0 dBV point, see FIG. 4. The equation forthe output of the log amp 46 is expressed as:

Vout=0.040x+2.95   (1)

where x is the value in dB of the input signal.

Equation (1) can be solved for x in volts (not dB) by rewriting equation(1) with dB:

Vout=Slope*[20*log(Vin)]+2.95   (2)

the slope from equation (1) equals 0.04, Vin equals the input voltage tothe log amp 46 and the 20 in equation (2) comes from the conversion ofdBV to V which is:

dBV=20*log(V)   (3)

solving for Vin:

Vin=10 ̂[(Vout−2.95)/(20*Slope)]  (4)

the power of 10 comes from the inverse of the log function.

With reference again to FIG. 3, the voltage signal into log amp 46 is avoltage divider using the ratio of C1 and C2. This voltage signal isequal to:

V _(—) RF=V_Out×(XC ₂/(XC ₂ +XC ₁)   (5)

where XC=1/(2πfC), V_Out is the output voltage of the generator 8, f isthe operating frequency of the generator 8, and C is the value of thecapacitors.

The current signal into the log amp 40 may be derived from measuring thevoltage integrated across the blocking capacitors “BC”. The voltageacross the blocking capacitor “BC” is related to the current through theblocking capacitor “BC” using the equation:

dv=I×dt/C   (6)

where I is the output current of the generator 8, C is the value of theblocking capacitor “BC”, dv is the change in voltage across thecapacitor “BC”, and dt is the switching cycle time.

In some embodiments, to reduce noise on the current signal, adifferential pair (not explicitly shown) may be run from the blockingcapacitors “BC” back to an input of the log amp 48. In particular, a lowpass differential filter (with a pole of suitable frequency, e.g., about100 KHz) may be added in series with the log amp 48. One or more lowpass differential filters may also be added in series with the log amp46 to facilitate reducing noise on the current signal.

The aforementioned configuration of the log amps 46 and 48 and low passfilter facilitates maintaining a consistent overall gain of themeasurement module 21.

To accurately control the electrosurgical energy applied to tissue, thecontroller 18 needs to accurately sense the voltage and current at thetissue. As noted above, however, the voltage sensed by the voltagesensor 38 and the current sensed by the current sensor 40 may beinaccurate because of the internal construction of the log amps 46 and48. In particular, log amps 46 and 48 may have an internal gain that isdependent on the input voltage such that the gain of the log amps 46 and48 is not constant across a dynamic range of the log amps 46 and 48. Thedynamic range of the log amps 46 and 48 may be measured from a voltageminimum (or current minimum) to a voltage maximum (or current maximum).This gain variation present for both log amps 46 and 48 may result indecreased accuracy of log amp sensors 38 and 40. In other words, thevoltage and current measured at the RF output stage 22 by the voltageand current sensors 38, 40 may not equal the actual voltage and currentat the load “L” (e.g., tissue) because of the non-linear gain dependencyat the inputs of the log amps 46 and 48.

The electrosurgical system 2 is configured to calibrate sensors 38 and40 to compensate for the gain losses of the log amps 46 and 48 thatintroduce errors into the sensor data provided by the sensors 38 and 40.In particular, a slope of the log amps 42 and 44 and an overall gain ofthe measurement module 21 is calculated via the calibration computersystem 16. In accordance herewith, the overall gain of the measurementmodule 21 takes into account the voltages from the capacitor dividernetwork, attenuation due to the filter, and the gain through the log amp38 and/or 40. For illustrative purposes, the overall gain of themeasurement module 21 is obtained using the gain of the log amp 46 thatrelates to measurements sensed by the voltage sensor 38.

The slope and gain are calculated via calibration computer system 16.Calibration computer system 16 is in connection with the controller 18of the generator 8 and includes a processor 50, a memory 52, and acommunications interface 54. Calibration computer system 16 utilizes oneor more suitable measuring devices to measure output voltage andcurrent. In the illustrated embodiment, a RMS meter 56 in communicationwith a current toriod 58 is utilized to measure output current Inns sentto the test load “L” as shown in FIG. 5. The output voltage

V rms can be obtained by multiplying the output current by theresistance of the test load “L.”

In some embodiments, the generator 8 is connected to the calibrationcomputer system 16, RMS meter 56 including the current toroid 58, and a100 ohm test load “L.” In this instance, for example, calibrationcomputer system 16 configures the generator 8 to operate in an open loopmode, sets a target value(s), and turns on the generator 8 until thegenerator reaches the target value(s). In some embodiments, the powersupply duty cycle of the generator 8 is varied to produce an RF outputfrom 4 volts rms to 92 volts rms, e.g., through the dynamic range of thelog amps 46 and 48. Calibration computer system 16 records the datameasured by the generator 8 and RMS current meter 56, see table (1) inFIG. 6. In embodiments, this data can be loaded into one or moresuitable templates, e.g., a formatted Excel template, for analysis of aload curve to plot error.

Table (1) in FIG. 6 lists the impedance of the test load “L”, e.g., a100 Ω load, measured Irms, V1raw (output voltage of log amp 46), I1raw(output current of log amp 48) and calculated V nns which is obtained bymultiplying a corresponding Irms by the test load “L” impedance (e.g.,0.893 A×100 Ω=89.3 V). The processor 50 accesses measurement data oftable (1) and stores the measurement data in the memory 32 of thegenerator 8. This data is accessible by the DSP 28 to execute one ormore control algorithms for controlling an output of the generator 8.

In some instances, the slope is calculated by dividing the dynamic rangeof the output of the voltage log amp 46 over the measured range of theoutput of the generator 8 in dB using the following equation:

Slope=(Log_(out) _(—) max−Log_(out) _(—) min)/((20×log(Gen_(out) _(—)max))−(20×log(Gen_(out) _(—) min)))   (7)

where Log_(out) _(—) max is the maximum output value of the log amp 38recorded (2.7979), Logout_min is the minimum value of the log amp 38recorded (1.6479, (0.3735 in this column is used to verify the offset ofthe log amp 46 at no output of the generator 8; this offset should bebetween 0.3 to 0.5)), Genout_max is the max output of the generator 8(89.3) and Genout_min is the min output of the generator 8 (3, (the 0may be ignored)). It has been found that the slope of the log amp 46 isequal to about 39 mV/dB and is linear over the dynamic range, as shownin FIG. 4, for example.

To measure the gain of the log amp 46 (e.g., overall gain of themeasurement module 21), first the output voltage of the log amp 46 istranslated to an input voltage, using the following equation:

Vin=10̂[(Vout−2.95)/(20*Slope)]  (8)

where the “slope” is the slope of the voltage log amp 46 and Vout is theVraw from table (1). The output of the log amp 46 equals 2.7979V at acalculated output voltage Vrms from the generator 8 of 89.3V. Placingthis into equation (4) and using the 39 mV for the slope, the inputvoltage is 0.638V, see Log V1 column of table (1) in FIG. 6; this is theactual voltage at the input of the log amp 46. The gain can now becalculated using the equation:

GainV=Calculated_(—) Vrms/Vin   (9)

in this instance the gain is equal to 139.88 (e.g., 89.3 v/.638 v). Thegain for each measured output voltage Vraw of the log amp 46 andcorresponding output voltage Vrms of the generator 8 can be calculatedin a similar manner and recorded. As can be appreciated, the moremeasurements taken through the dynamic range of the log amp 46 the moreaccurate the calculate gain will be. Multiplying equation (4) with thegain calculated in equation (9) gives an accurate representation of theoutput of the generator 8 referenced to the output of the log amp 46when the generator 8 is coupled to a test load, see equation (10) below.

Out=Gain*10̂[(Vout−2.95)/(20*Slope)]  (10)

Equation (10) is stored in memory 32 and, in some instances, may beutilized in a control algorithm by the DSP to calculate the output ofthe generator 8 in a real time scenario.

As can be appreciated, the Vrms is, however, not measured with anexternal device, e.g., an RMS meter 56, in a real time scenario. Asnoted above, the gain of the log amp 46 (and/or log amp 48) is notconstant across the dynamic range, see FIG. 6 for example under the V1Gain column. The gain value changes from 132 to 140 in a non-linearrelation. This gain variation is prevalent for both log amps 46 and 48.Therefore, in a surgical environment, the DSP 28 utilizes one or morecontrol algorithms to calculate the gain to calibrate the sensor 38and/or sensor 40. The DSP 28 uses the above data to fully automate thecalibration of the sensor 38 (and/or sensor 40) by calculating the slopeof the log amp 46 (and/or log amp 48) utilizing one or more of theaforementioned equations. The overall gain of the measurement module 21is subsequently calculated and utilized by the DSP 28 to accuratelycalculate the Vrms, impedance and/or the power at the tissue site.

In particular, and in one embodiment, the calibration computer system 16utilizes a control algorithm that incorporates a piece-wise linear fitof the gain relative to the measured output of the log amp 46 to correctthe variations in gain of the log amp 46. In this instance, for example,the data of table (1) may be stored into memory 22 and accessed by theDSP 28. When the output of the voltage log amp 46 detected by the DSP 28falls between two known values the gain is calculated using a linearslope equation:

Gain_Calc=mX+b   (11)

in this equation Gain_Calc is the calculated gain value, X is the V1rawdata from table (1), m is the slope between the two known gain points,and b is a calculated offset. It should be noted that the “Gain_Calc” inequation (11) is not the same as the “Gain” in equation (10). Gain_Calc”is the gain between two gain values (e.g., 134.96 and 140.27) previouslycalculated and stored into memory 22. For example, if the detectedoutput from the log amp 46 is 2.10, which falls between an output of logamp 46 that equals 1.96 (see table (1) in FIG. 5) and an output of thelog amp 46 that equals 2.24 (see table (1) in FIG. 5) the DSP 28utilizes equation (11) below and the corresponding gains to calculatethe Gain_Calc.

m=(Gain2−Gain1)/(Log_out2−Log_out1)   (11)

To calculate m, Gain 1 is a first gain point (134.96), which correspondsto an output of the log amp 46 that equals 1.96 and Gain 2 is a secondgain point (140.27), which corresponds to an output of the log amp 46that equals 2.24 (see FIG. 6). Log_out1 is the output of the voltage logamp 46 in relation to the first gain point (1.96) and Log_out2 is theoutput of the voltage log amp 46 in relation to the second gain point(2.24), see FIG. 6. In this example, m is equal to 18.96.

b=Gain1−m*(Log_out1)   (12)

Continuing with the present example, and using equation (12) above, b iscalculated to be equal to 97.8.

Taking the values found for b and m and using them in equation (11), thecorresponding output of the log amp 46 is equal to 2.10 and the gain isfound to be equal to 137.62.

The DSP 28 utilizes this gain value of 137.62 in equation (10) toaccurately calculate Vrms, impedance and/or the power at the tissuesite. The slope is assumed to equal 39 mV. The calculated value of thegain (137.62) is substituted into equation (10), Vrms is calculated tobe (137.62)10̂[(2.10−2.95)/(20×0.039)], which is equal toVrms=(137.62)10 ̂(−0.85/0.78), which is equal to Vrms=(137.62) 10̂(−1.089), which is equal to Vrms=11.192. This value of Vrms fallsbetween the previously measured Vrms values 17.1 and 7.3 that correspondto the outputs 2.24 and 1.96 of the log amp 46.

In some embodiments, the calibration computer system 16 utilizes acontrol algorithm that incorporates an averaging technique of the gainrelative to the measured output of the log amp 46 to correct thevariations in gain of the log amp 46. In this instance, the log amp 46gain values from the individual calibration points across the dynamicrange are averaged together to get a mean gain for the error over thedynamic range of the voltage log amp 46. In this instance, the DSP 28calculates the mean gain value over the dynamic range and substitutesthis gain in equation (10) and then calculates the Vrms (or otherdesired parameter at the tissue site).

In some embodiments, the calibration computer system 16 utilizes acontrol algorithm that incorporates a polynomial curve fitting technique(“poly-fit” technique) of the gain relative to the measured output ofthe log amp 46 to correct the variations in gain of the log amp 46. Inthis instance, one or more suitable polynomials may be utilized torepresent the gain variations of the voltage log amp 46. For example, atypical third order polynomial:

V=a*Vcalc^(̂3) +b*Vcalc^(̂2) +c*Vcalc+d

where a, b, c, and d are the polynomial calibration coefficients may beutilized to represent the gain variations of the voltage log amp 46.

Operation of the electrosurgical system 2 is described with reference tothe piece-wise linear fit algorithm. In this instance, it is assumedthat the data of table (1) has been previously calculated for the logamp 46 and stored into memory 32 of the main processor 30.

In use, the DSP 28 receives an output, e.g., an output voltage, from thelog amp 46. DSP 28 runs through the piece-wise linear fit controlalgorithm to calculate a gain of the log amp 46. Thereafter, the Vrms iscalculated utilizing the calculated gain in equation (10). Once the Vrmsis calculated, the DSP 28 can communicate control signals as needed toensure that the generator 8 provides a correct amount of electrosurgicalenergy to the forceps 4.

The electrosurgical system 2 including the generator 8 and calibrationcomputer system 16 provides an effective method of calibrating thesensors 38 and 40 to overcome the aforementioned drawbacks that aretypically associated with conventional generators.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the same. For example, various temperature ranges could utilize theirown multi-point calibrations to compensate for any temperaturedependency of the log amp 46 and/or log amp 48.

Moreover, it is within the purview of the instant disclosure to utilizea plurality of log amps 46 and a plurality of log amps 48. As can beappreciated, this adds an extra layer of sensing capabilities, which, inturn may increase overall gain of the measurement module 21.

Further, the aforementioned control algorithms may utilized incombination with one another. For example, the DSP 28 may utilize apiece-wise linear control algorithm across a first portion of thedynamic range of the log amps 46 and 48 and may utilize the averaging(or poly-fit) control algorithm across a second, different portion ofthe dynamic range of the log amps 46 and 48.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of particular embodiments. Those skilled in the artwill envision other modifications within the scope and spirit of theclaims appended hereto.

1-14. (canceled)
 15. A computer calibration system for calibratingmeasurement circuitry of an electrosurgical device, the computercalibration system comprising: a measurement device configured tomeasure an output of the electrosurgical device; a memory that storesmeasurement data including a plurality of current and voltage values ofat least one log amp of the measurement circuitry, a plurality of gainvalues of the log amp, a plurality of current and voltage values of theelectrosurgical device, and a plurality of impedance values of a loadcoupled to the electrosurgical device; a processor configured to executeat least one control algorithm to compile the measurement data into atleast one data look-up table; and a communication interface configuredto transfer the at least one data look-up table to a memory of theelectrosurgical device.
 16. The computer calibration system according toclaim 15, wherein the at least one log amp is configured to receive anoutput from a sensor configured to sense an output of theelectrosurgical device.
 17. The computer calibration system according toclaim 15, wherein the measurement device is an RMS current sensingdevice, wherein the measurement device includes a current sensing toroidthat is configured to measure an output current of the electrosurgicaldevice.
 18. A method for calibrating measurement circuitry of anelectrosurgical device, comprising measuring an output of theelectrosurgical device; measuring an output of at least one log amp of ameasurement circuitry of the electrosurgical device; compiling a datalook-up table including measurement data based on the output of theelectrosurgical device and the at least one log amp; calculating a slopeand a gain of the at least one log amp based on the measurement data;executing at least one control algorithm utilizing the calculated slopeand gain; and recalculating a gain of the log amp based on an output ofthe log amp to calibrate the measurement circuitry.
 19. The methodaccording to claim 18, wherein the at least one control algorithmutilizes a piece-wise linear fit of the gain relative to the measuredoutput of the log amp to correct gain variations of the log amp.
 20. Themethod according to claim 18, wherein the at least one control algorithmutilizes one of an averaging technique or a polynomial curve fittingtechnique of the gain relative to the measured output of the at leastone log amp to correct for variations in the gain.
 21. The computercalibration system according to claim 15, wherein the processor isconfigured to calculate a slope and a gain of the at least one log amp.22. The computer calibration system according to claim 21, wherein theslope and the gain of the at least one log amp are calculated based on adynamic operating range of the at least one log amp.
 23. The computercalibration system according to claim 22, wherein the at least one logamp is adjustable to obtain an optimum slope through the dynamicoperating range.
 24. The computer calibration system according to claim21, wherein the control algorithm utilizes a piece-wise linear fit ofthe gain relative to an output of the at least one log amp to correctgain variations of the at least one log amp.
 25. The computercalibration system according to claim 21, wherein the control algorithmutilizes an averaging technique of the gain relative to an output of theat least one log amp to correct gain variations of the at least one logamp.
 26. The computer calibration system according to claim 21, whereinthe control algorithm utilizes a polynomial curve fitting technique ofthe gain relative to an output of the at least one log amp to correctgain variations of the at least one log amp.